Formation of silicon carbide-silicon nitride nanoparticle carbon compositions

ABSTRACT

A composition having nanoparticles of silicon carbide and a carbonaceous matrix or silicon matrix. The composition is not in the form of a powder. A composition having silicon and an organic compound having a char yield of at least 60% by weight or a thermoset made from the organic compound. A method of combining silicon and the organic compound and heating to form silicon carbide or silicon nitride nanoparticles.

This application claims the benefit of U.S. Provisional Application No.61/693,930, filed on Aug. 28, 2012. This application is a continuationin part application of U.S. Nonprovisional patent application Ser. No.13/779,771, filed on Feb. 28, 2013, which is a continuation in partapplication of U.S. Nonprovisional patent application Ser. No.13/768,219, filed on Feb. 15, 2013, which is a continuation in partapplication of U.S. Nonprovisional patent application Ser. No.13/749,794, filed on Jan. 25, 2013, which claims priority to U.S.Provisional Application No. 61/590,852, filed on Jan. 26, 2012, U.S.Provisional Application No. 61/640,744, filed on May 1, 2012, U.S.Provisional Application No. 61/669,201, filed on Jul. 9, 2012, and U.S.Provisional Application No. 61/693,930, filed on Aug. 28, 2012. Theseapplications and all other publications and patent documents referred tothroughout this nonprovisional application are incorporated herein byreference.

TECHNICAL FIELD

The present disclosure is generally related to synthesis of siliconcarbide and silicon nitride.

DESCRIPTION OF RELATED ART

Silicon carbide is one of the most important carbides used in industry.Silicon carbide exists in two main crystal modifications: the hexagonal(α-SiC) and cubic (β-SiC). The hexagonal modification is a “giantmolecule,” constructed in accordance with the principle of a uniquestructurally directed polymerization of simple molecules. The layers ofcarbon and silicon atoms in α-SiC are arranged in various ways withrespect to one another, thus forming many structural types. Thetransition from β-SiC to α-SiC occurs at 2100°-2300° C. (the reversetransition is usually not observed). Silicon carbide is refractory(melts with decomposition at 2830° C.) and is extremely hard beingsecond only to diamond and boron carbide, B₄C. It is brittle and itsdensity is 3.2 g/cm³. Silicon carbide is stable in various chemicalmedia even at high temperatures.

Silicon carbide can be produced by heating silica sand (SiO₂) and carbonby the Acheson process to high temperatures in a high temperaturefurnace. In an Acheson graphite electric resistance furnace, theproduced SiC is suitable for grinding and cutting applications attemperatures above 2200° C. A furnace run can last several days, duringwhich temperatures vary from 2200° to 2700° C. in the core to about1400° C. at the outer edge. The energy consumption exceeds 100,000kilowatt-hours per run. At the completion of the run, the productconsists of a core of green to black SiC crystals loosely knittedtogether, surrounded by partially or entirely unconverted raw material.The lump aggregate is crushed, ground, and screened into various sizesappropriate depending on the end use. Widely used as an abrasivematerial, SiC is marketed under such familiar trade names asCARBORUNDUM® and CRYSTOLON®. It is heat resistant, decomposing whenheated to about 2700° C. It is used in refractory applications, e.g.,rods, tubes, firebrick, and in special parts for nuclear reactors. Verypure silicon carbide is white or colorless; crystals of it are used insemiconductors for high-temperature applications. Silicon carbidefibers, added as reinforcement to plastics or light metals, impartincreased strength and stiffness.

For special applications, silicon carbide is produced by a number ofadvanced processes. Reaction-bonded silicon carbide is produced bymixing SiC powder with powdered carbon and a plasticizer, forming themixture into the desired shape, burning off the plasticizer, and theninfusing the fired object with gaseous or molten silicon, which reactswith the carbon to form additional SiC. Wear-resistant layers of SiC canbe formed by chemical vapor deposition, a process in which volatilecompounds containing carbon and silicon are reacted at high temperaturesin the presence of hydrogen in a closed reactor. For advanced electronicapplications, large single crystals of SiC can be grown from the vaporand then sliced into wafers much like silicon for fabrication intosolid-state devices. For reinforcing metals or other ceramics, SiCfibers can be formed in a number of ways, including chemical vapordeposition and the firing of silicon-containing polymer fibers.

In shaped components, SiC is brittle and is fabricated from the powderby the sintering technique at high temperature and pressure. Theconventional carbothermal reduction method for the synthesis of SiCpowders is an excessive demanding energy process and leads to a ratherpoor quality material. Grains of silicon carbide can be bonded togetherby sintering of the produced powder from reaction of silica with carbonto form very hard ceramics, which are widely used in applicationsrequiring high endurance, such as car brakes, car clutches, and ceramicplates in bulletproof vests. In addition, it has low impact resistanceand low fracture toughness.

Electronic applications of silicon carbide as light emitting diodes anddetectors in early radios were first demonstrated around 1907, andcurrently SiC is widely used in high temperature-high voltagesemiconductor electronics. Large single crystals of silicon carbide canbe grown by the Lely process, in which SiC powder is sublimated in anargon atmosphere at 2500° C. and redeposited into flake-like singlecrystals on a slightly colder substrate. Current SiC devices includeSchottky barrier diodes, solid state circuit breakers, power modules,and custom SiC integrated circuits. Currently, SiC Schottky diodes arethe only SiC power devices sold in large volumes.

Several recent technical and market reports have recognized siliconcarbide power electronics as a potential technology for solar and windturbine power converters. The primary benefits of SiC-based powerdevices include low losses, high temperature tolerance, and fastswitching. In essence, SiC can be exploited to reduce generation lossesand increase net energy production. The low losses and high temperaturetolerance can also be used to improve the reliability of the converterand reduce the thermal management requirements. Moreover, fast switchinghas the potential to reduce the filtering passive component size andcost and thus, the total cost of the system.

Ceramic materials such as silicon carbide and silicon nitride continueto be used to fabricate specific high temperature automobile enginecomponents and brakes for automobile vehicles and aircraft and as a wayto improve the performance of gas-turbine engines for aircraft tolengthen their life span and reduce their fuel consumption. Thechallenges involved have been considerable. The material in modernturbines must survive temperatures of more than 1100° C. for thousandsof hours, high thermal stresses caused by rapid temperature changes andlarge temperature gradients, high mechanical stresses, isolated impactand contact stresses, low- and high-frequency vibrational loading,chemical reactions with adjacent components, oxidation, corrosion, andtime- and stress-dependent effects such as creep, stress rupture, andcyclic fatigue. Early ceramic materials were not able to withstand theseconditions and early turbine-component designs were not compatible withbrittle materials. Technological evolution has to be made over a broadfront and progress has been slow. Silicon carbide and silicon nitrideare currently heavily used for turbine engine applications due to theirsuperb thermal shock resistance, largely due to a combination of lowthermal expansion, high strength, and moderate thermal conductivity.

Ceramic turbine components are fabricated starting with powders of theraw materials of which SiC is a major source. The quality of the finalpart depends on the quality of the starting powder and on each step inthe fabrication process under sintering conditions. Sintered siliconnitride and silicon carbide materials have become the primary candidatesfor turbine engine programs. These materials have intermediate strengthsbetween reaction-bonded and hot-pressed materials, but they have thepotential to be fabricated to near-net shape at costs competitive withmetal turbine components. Most of the effort has focused oninjection-molding and slip-casting radial turbine rotors, scrolls, andother turbine components. More recently, researchers have demonstratedthat silicon nitride and silicon carbide can be densified bypressureless sintering if the starting powders are of very smallparticle size.

BRIEF SUMMARY

Disclosed herein is a composition comprising: nanoparticles of siliconcarbide; and a carbonaceous matrix or silicon matrix. The composition isnot in the form of a powder.

Also disclosed herein is a composition comprising: silicon; and anorganic component selected from an organic compound having a char yieldof at least 60% by weight and a thermoset made from the organiccompound.

Also disclosed herein is a method comprising: combining silicon and anorganic compound having a char yield of at least 60% by weight to form aprecursor mixture.

Also disclosed herein is a method comprising: providing a precursormixture of silicon and an organic compound; heating the precursormixture in an inert atmosphere at elevated pressure and at a temperaturethat causes polymerization of the organic compound to a thermoset toform a thermoset composition; and heating the thermoset composition inan inert atmosphere, argon, nitrogen, or vacuum at a temperature thatcauses formation of a ceramic comprising nanoparticles of siliconcarbide or silicon nitride in a carbonaceous matrix or silicon matrix.The organic compound has a char yield of at least 60% by weight whenheated at the elevated pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention will be readily obtainedby reference to the following Description of the Example Embodiments andthe accompanying drawings.

FIG. 1 schematically illustrates a process for forming the disclosedcompositions.

FIG. 2 schematically illustrates silicon particles 10 embedded in athermoset matrix 20.

FIG. 3 schematically illustrates the transfer 40 of carbon atoms fromthe carbon matrix 30 to the silicon 50.

FIG. 4 schematically illustrates silicon carbide nanoparticles 60 in acarbonaceous matrix 70.

FIG. 5 shows an X-ray diffraction analysis (XRD) of a sample containingSiC nanoparticles in a silicon matrix.

FIG. 6 shows an XRD of a sample containing SiC and Si₃N₄ nanoparticlesin a silicon matrix.

FIG. 7 shows an XRD of a sample containing SiC nanoparticles in asilicon matrix.

FIG. 8 shows a scanning electron micrograph (SEM) of a sample containingSiC nanoparticles.

FIG. 9 shows an XRD of a sample containing SiC nanoparticles in asilicon matrix.

FIG. 10 shows an XRD of a sample containing SiC nanoparticles in acarbon matrix.

FIG. 11 shows a photograph of a sample containing SiC and SiBCnanoparticles.

FIG. 12 shows an SEM of a sample containing SiC and SiBC nanoparticles.

FIG. 13 shows a photograph of a sample containing nearly pure SiCnanoparticles.

FIG. 14 shows an XRD of a sample containing nearly pure SiCnanoparticles.

FIG. 15 shows a photograph of a carbon fiber-reinforced samplecontaining SiC nanoparticles.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In the following description, for purposes of explanation and notlimitation, specific details are set forth in order to provide athorough understanding of the present disclosure. However, it will beapparent to one skilled in the art that the present subject matter maybe practiced in other embodiments that depart from these specificdetails. In other instances, detailed descriptions of well-known methodsand devices are omitted so as to not obscure the present disclosure withunnecessary detail.

Disclosed herein is (1) a method for the in situ formation ofnanoparticle silicon carbide (SiC) and nanoparticle silicon nitride(Si₃N₄) from reaction of elemental silicon particles with a meltablecarbon precursor with or without a carbon matrix in one step affording ashaped composition with structural integrity, (2) various elementalsilicon-carbon precursor/thermoset compositions at multiple stages, (3)various nanoparticle silicon carbide-carbon matrix compositions, (4)various nanoparticle silicon nitride-carbon matrix compositions, (5)fiber reinforced silicon-carbide and silicon carbide-carbon matrixcomposites, and (6) fiber reinforced silicon nitride-carbide and siliconnitride-carbon matrix composites.

Also disclosed herein are (1) a method for the in situ formation ofnanoparticle SiC and nanoparticle Si₃N₄ from reaction of excesselemental silicon particles with a meltable carbon precursor with asilicon matrix in one step affording a shaped composition withstructural integrity, (2) various elemental silicon-carbonprecursor/thermoset compositions with excess silicon at multiple stages,(3) various nanoparticle silicon carbide-silicon matrix compositions,(4) various nanoparticle silicon nitride-silicon matrix compositions,(5) fiber reinforced silicon-carbide and silicon carbide-silicon matrixcomposites, and (6) fiber reinforced silicon nitride-carbide and siliconnitride-silicon matrix composites.

In the methods disclosed herein, elemental powder silicon is combinedwith a carbon precursor. When the same reaction is performed in a flowof nitrogen, silicon nitride (outer surface) and silicon carbide(interior)-carbon matrix compositions are also formed in astoichiometric array. The carbon precursors are compounds such aspolymers or resins with functional unsaturation to permit the carbonprecursor to undergo conversion from the melt to form shaped thermosetsor crosslinked polymers and upon conversion to carbon exhibit high charyields. A typical composition includes the carbon precursor and theelemental silicon powder. Upon heating the composition, the carbonprecursor melts at its melting point and is thermally converted to ashaped solid thermoset through reaction of the unsaturated sites. Toremove entrapped air pockets and thus obtain a fully dense, void-freethermoset, the shaped thermoset composition can be consolidated underpressure and/or vacuum, which will also bring the reactants (silicon andcarbon atoms) during the thermal treatment above 500° C. into intimatecontact for the reaction to readily occur to afford the ceramicnanoparticle solid composition. Thermal treatment of the shapedthermoset above 500° C. and to about 1450° C. results in carbonizationof the carbon precursor yielding carbon atoms that react in an argonatmosphere with the silicon particles affording the silicon carbidenanoparticles, which are embedded in the excess carbon.

To obtain the high surface area silicon carbide nanoparticles, it isimportant that the reaction be performed at a very slow heat up rateespecially at and above the melting point of the silicon to ensure acontrolled exothermic reaction. The temperature can be held for anextended time at various temperatures above the melting point so thatthe silicon completely melts to ensure a smooth reaction of the siliconwith the carbon in a controlled manner. The slow heat-up rate ensuresthat the carbon atoms interact with the silicon before and after themelting of the silicon. When melted, silicon reacts with the carbon veryrapidly and when heated very slowly, nanosized silicon carbide particlesare formed. Faster heating rates can be used up to the melting point ofthe silicon before the reaction readily occurs.

The temperatures at which the synthetic process occurs are well belowthose normally associated with the formation of silicon carbide andnitride ceramics from reaction of the silicon source with graphiticcarbon. By its very nature, the method permits the carbide- ornitride-carbon composites to be easily shaped by molding procedures(injection molding, vacuum molding, pressure molding, spreading, etc),which is a far less costly and involved process than machining a hotpress sintered material.

The present methods can create carbides or nitrides as nanoparticlesfrom reaction of elemental silicon in a controlled manner with ameltable carbon precursor with fast reaction of the “hot” carbon atomsbeing formed during the carbonization process and reacting with thesilicon near the melting point to afford silicon carbide nanoparticles(argon atmosphere) within a relatively narrow size range and withsilicon nitride nanoparticles (nitrogen atmosphere) being formed on theexterior portion of the solid ceramic exposed to nitrogen gas. Thinfilms of silicon nitride nanoparticles within a carbon matrix can alsobe formed.

An excess of carbon ensures the formation of a carbon matrix in whichthe silicon carbide nanoparticles are embedded, or the reaction can beconducted stoichiometrically to yield only silicon carbidenanoparticles. Heating of this composition to even higher temperaturesat least to 2000° C. or greater should enhance the physical propertiesof the formed ceramic due to the migration of atoms of silicon andcarbon from the individual nanoparticles, which is a form of fusion orbonding of the particles. The amount of silicon carbide and carbonwithin the resulting composition can be varied based on the quantity ofeach individual component (elemental silicon and melt processable carbonresin) mixed for usage in the precursor composition. When the reactionis performed in a nitrogen atmosphere, the silicon preferentially reactswith the nitrogen, especially on the exterior part of a shapedcomponent, relative to the carbon affording the corresponding siliconnitride in pure form. Nitrogen cannot progress very far into the solidshaped sample ensuring silicon carbide formation in the interior portionof any thick solid component. If silicon is presence in excess amountrelative to the carbon, all of the above applies except that the formedceramic silicon carbide nanoparticles are embedded in glassy silicon.This may limit the usage of the solid composition below 1400° C.

Regardless of the ratio of elemental silicon to carbon source, thesilicon carbides or nitrides form as nanoparticles. This is a highlydesirable result, as it is generally accepted that homogeneousnanoparticle composites of ceramics will have better properties thantheir much more common microparticle counterparts. Moreover, newtechnologies that do not presently exist could become important due tothe higher surface area, more reactive silicon carbide nanoparticles.The interaction of the nanoparticles with each other and the ability topack tightly would favorably enhance the physical properties relative tomicrosized particles.

Carbon, ceramic, and metal fibers may be incorporated into variousmixtures of precursor compositions composed of elemental silicon and theacetylenic-containing aromatic compounds or polymers (carbon source) andthe resulting fiber-containing mixture is converted to a shaped solid attemperatures below 500° C., followed by heating to temperatures ≧1400°C. yielding a carbon-fiber reinforced silicon carbidenanoparticle-carbon matrix composite. The precursor composition(elemental silicon and carbon precursor) described above are mixed withcontinuous carbon fibers or chopped carbon fibers and heated untilconversion to the shaped thermoset forms. The fibers may also be, forexample, metal or ceramic. Heating of the carbon-fiber reinforcedthermoset above 500° C. and ≧1400° C. in an inert atmosphere (argon)results in the formation of the carbon fiber reinforced siliconcarbide-carbon matrix composites. The toughened, solid carbon fiberceramic composite can be used for structural and electronic applications(e.g., flak jacket/bullet proof vest, automobile and aircraft brakes,high temperature/high voltage semiconductor electronics up to 600° C.,and nuclear reactors). The precursor composition can contain variouscombinations of elemental silicon and carbon precursor that will lead toshaped ceramics with numerous amounts of silicon carbide nanoparticlesembedded in a carbon or silicon matrix composite, which could bebeneficial for specific applications. For application above 1400° C.,the carbon should be presence in excess or in a stoichiometric amountwith the silicon to ensure 100% yield of silicon carbide or siliconnitride formation or combination thereof. In all cases, precursorcompositions containing non-stoichiometric amounts with silicon inexcess ensure the formation of the silicon ceramic nanoparticlesembedded in a silicon matrix and usage below 1400° C. due to the meltingpoint of silicon at around 1400° C.

As noted above, when the elemental silicon and carbon precursorcomposition with carbon in excess are heated in a nitrogen atmosphere,silicon nitride nanoparticles form as a layer on the exterior portion ofthe ceramics. Therefore, another composition would be the formation ofsilicon nitride-carbon matrix compositions, which is a directinteraction of nitrogen with the silicon atoms of the precursor siliconforming silicon nitride nanoparticles. Thus, by changing the atmospherefor performing the reaction, one can selectively form either thesilicon-carbide carbon matrix composition or the silicon-nitride carbonmatrix composition or combinations thereof. When the fiber-containingprecursor compositions are heated in a nitrogen atmosphere on thinfilms, fiber reinforced silicon nitride-carbon matrix composites will beformed. Regardless of the inert atmosphere (argon or nitrogen), thecomposite may have outstanding oxidative stability and temperaturecapabilities in excess of 3000° C. when carbon is the matrix material.

The synthetic method may produce silicon carbides (SiC) and siliconnitrides (Si₃N₄) in shaped solid configurations from reaction ofelemental silicon with a meltable carbon precursor, exhibiting anextremely high char yield, at elevated temperatures above 600° C. Mixedphases of SiC and Si₃N₄ can also be produced. The SiC and Si₃N₄ can beproduced as nanoparticles from the slow reaction of silicon at thebeginning of the melting point temperature of silicon with carbon atomsin argon and nitrogen atmospheres, respectively, during the pyrolysisreaction. When (a) powdered silicon even in micro sized particles iscombined with (b) carbon precursors that melt and only contain carbonand hydrogen followed by (c) heating to a temperature that converts theprecursor into a solid thermoset in which the silicon is homogeneouslyembedded within the solid composition and the combination can be (d)thermally converted to a solid shaped ceramic solid containing highyields of pure silicon carbide nanoparticles or silicon nitridenanoparticles or combinations thereof depending on whether the reactionis performed in argon or nitrogen. The appropriate silicon nanoparticleceramics are formed in situ from the interaction of the siliconparticles with the carbon atoms of the carbon precursor or with nitrogenduring the thermal treatment from 600-1600° C., 600-1900° C., or togreater than 1900 or 2000° C. At 1450° C., the cubic β-SiC is formed butby heating the SiC nanoparticles to temperatures in excess of 2000° C.,the hexagonal α-SiC phase may be produced. Small amounts of α-SiC mayalso be produced at lower temperatures as evidenced by the small peaksor shoulders at 34° in the XRDs FIGS. 5, 7, 9, and 10. The particle sizeof silicon-based ceramic can be controlled as a function of thetemperature heat-up rate and the upper heated temperature and whetherthe reaction of silicon with carbon occurs in the silicon melt whileheating rapidly (large nanoparticle to microsized SiC) to highertemperatures or at the beginning silicon melt (nanoparticle size SiC)temperature and slowly heating in a controlled manner. The siliconparticles do not readily react with the carbon or nitrogen until nearthe melting or after the melting of the silicon. The carbon sources aremelt processable aromatic-containing acetylenes, e.g.1,2,4,5-tetrakis(phenylethynyl)benzene (TPEB), or low molecular weightpolymers that exhibit extremely high char yields to ensure high density,void-free solid components. The carbon precursor may contain only C andH to insure that pure silicon carbide and silicon nitride are producedcontrollably during the reaction. The silicon carbide and/or siliconnitride nanoparticles form around the melting point of silicon with thereaction occurring faster at higher temperatures in the melt affordinglarger particle sizes of the ceramic. When an excess of the carbonprecursor is used, the individual formed ceramic nanoparticles (siliconcarbide or silicon nitride) are glued or bound together with theresulting nanostructured or amorphous elastic carbon to affordstructural integrity. The overall properties of the ceramics can betailored as a function of the amount of the reactants (silicon powderand carbon source) used in precursor composition.

In addition as stated above, when an excess of silicon is used so thatall of the carbon atoms are reacted, the silicon carbide nanoparticlesare embedded in a matrix of silicon. Depending on the application, themethod allows for the silicon carbide nanoparticles to be embedded ineither carbon or silicon. Thus, the silicon carbide/nitride compositionscan be easily tailored to have various amounts of the matrix material(carbon or silicon) to essentially a composition of pure silicon carbideor silicon nitride or combinations thereof.

The process is outlined in FIG. 1 and schematically illustrated in FIGS.2-4. Any reactions described are not limiting of the presently claimedmethods and compositions. Even though microsized silicon powder is usedin the reaction, the silicon carbide and silicon nitride may be producedas nanoparticles from the reaction of the highly reactive carbon atom,being produced during pyrolysis (carbonization) of the carbon precursor,with the activated silicon surface, thereby lowering the temperature ofSiC or Si₃N₄ formation. Moreover, by varying the amount of elementalsilicon, which forms reactive silicon ceramic nanoparticles relative tothe carbon precursor, the amount of SiC or Si₃N₄ can be readily changedwith respect to the amount of carbon matrix in order to vary theproperties of the resulting solid composition. Thenanoparticle-containing SiC or Si₃N₄ carbon-matrix composites areexpected to exhibit unique physical properties such as hardness,toughness, and electrical conductivity, owing to the high surface areaof the nanoparticles and the presence of the relatively elastic carbon,which would exist in forms ranging from amorphous to nanotube tographitic carbon and are thermally stable to temperatures in excess of3000° C.

The native presence of an “elastic” carbon matrix allows for tougheningof the inherently brittle sintered ceramics and the isolation of theceramic nanoparticle within the matrix material. The pure SiC could bereadily consolidated to a tough, hard refractory ceramic by pressurelesssintering techniques at elevated temperatures (>2000° C.). The carbonpermits operation of the toughened ceramic at extremely hightemperatures, owing to carbon's high melting point (>3000° C.).Ceramic/carbon-matrix compositions are currently being sought for thesereasons, and the present method may permit straightforward preparationof shaped solid composites in a single step for the first time, incontrast to the traditional means of first forming the ceramic powderand then preparing the carbon-matrix composite under sinteringconditions. Also, the ratio of ceramic to carbon is easily tuned basedonly on the ratio of elemental silicon powder to carbon-precursor.Potential applications for these materials include structural enginecomponents, automobile components such as brake rotors, electricalcomponents and devices, armor, and solar panels.

Fiber or carbon fiber-reinforced silicon carbide and silicon nitridecarbon matrix composites can be fabricated in one step to a shapedcomponent and may exhibit outstanding mechanical and hardness propertiesfor usage under extreme environmental high temperature conditions. SuchSiC-based materials do not currently exist. Finely divided fiberreinforced silicon ceramic carbon composites may allow the consolidationof fully dense, shaped, low density, solid components with extremefracture resistance for uses in high stress and temperature applicationssuch as advanced engine components for aircraft and automobiles, whereincreased operation temperature and mechanical integrity could translateinto tremendous economic advantages. Such tough, easily shaped ceramiccomposites could be significant to the next generation of army tanks andother armor vehicles, which can be designed to be more energy efficientand lighter weight than those in current service. In addition, a morerobust nuclear reactor could be readily fabricated for aircraft carriersneeding the superior processability of tough structural rods and housingof the heat resistant silicon carbide or silicon nitride ceramic-carboncomposites. Also, lightweight, tough, and hard ceramics easily made incontrollable forms could be very important for the fabrication ofadvanced armor, energy storage and power electronic devices, ceramicplates in bulletproof vests, high performance “ceramic” brake discs,high-temperature gas turbines, nuclear rod/structural application inwhich the components are fabricated in a mold in a shaped structure. Itshigh thermal conductivity, together with its high-temperature strength,low thermal expansion, and resistance to chemical reaction, makessilicon carbide valuable in the manufacture of high-temperature bricksand other refractories. It is also classed as a semiconductor, having anelectrical conductivity between that of metals and insulating materials.This property, in combination with its thermal properties, makes SiC apromising substitute for traditional semiconductors such as silicon inhigh-temperature applications. A longstanding use of conductive ceramicsis as heating elements for electric heaters and electrically heatedfurnaces. Conductive ceramics are especially effective at elevatedtemperatures and in oxidizing environments where oxidation-resistantmetal alloys fail. The ability to fabricate tough, shaped siliconcarbide or silicon nitride components in one step enhances theirimportance due to the economic advantages and the elimination ofmachining to a shaped component.

In the first step of the method, two components are combined and may bethoroughly mixed. The first component is silicon in elemental form.Suitable silicon is readily available in powder form in >99% purity. Thesilicon powder may be milled to reduce its particle size. Milling to assmall a particle size as possible may improve the final product.

The second component is an organic compound that has a char yield of atleast 60% by weight. The char yield may also be as high as at least 70%,80%, 90%, or 95% by weight. The char yield of a potential compound maybe determined by comparing the weight of a sample before and afterheating to at least 1000° C. for at least 1 hr in an inert atmospheresuch as nitrogen or argon. Any such compounds with high char yields maybe used as the charring may play a role in the mechanism of thereactions. This char yield may be measured at an elevated pressure to beused when a heating step is also performed at such pressure. Thus, acompound having a low char yield at atmospheric pressure but having ahigh char yield under external pressure or the conditions that thedisclosed methods are performed may be suitable for producing siliconcarbides and silicon nitrides.

Certain organic compounds may exhibit any of the followingcharacteristics, including mutually consistent combinations ofcharacteristics: containing only carbon and hydrogen; containingaromatic and acetylene groups; containing only carbon, hydrogen, andnitrogen or oxygen; containing no oxygen; and containing a heteroatomother than oxygen. It may have a melting point of at most 400° C., 350°C., 300° C., 250° C., 200° C. or 150° C. and the melting may occurbefore polymerization or degradation of the compound or it may be aliquid. Examples of organic compounds include, but are not limited to,1,2,4,5-tetrakis(phenylethynyl)benzene (TPEB), 4,4′-diethynylbiphenyl(DEBP), N, N′-(1,4-phenylenedimethylidyne)-bis(3-ethynylaniline) (PDEA),N,N′-(1,4-phenylenedimethylidyne)-bis(3,4-dicyanoaniline)(dianilphthalonitrile), and 1,3-bis(3,4-dicyanophenoxy)benzene(resorcinol phthalonitrile) or a prepolymer thereof. More than oneorganic compound may be used. Prepolymers may also be used, such as aprepolymer of TPEB or other suitable organic compounds. Differentcompounds can be blended together and/or reacted to a prepolymer stagebefore usage as the organic compound of the precursor composition. Thepresence of nitrogen atoms in the organic compound may produce metalnitrides in the ceramic without the use of a nitrogen atmosphere.

An optional component in the precursor materials is a plurality offibers or other fillers. Examples of fibers include, but are not limitedto, carbon fibers, ceramic fibers, and metal fibers. The fibers may beof any dimension that can be incorporated into the mixture and may becut or chopped to shorter dimensions.

Another optional component is boron for formation of silicon boroncarbide nanoparticles. Suitable boron is readily available in powderform. A 95-97% boron is suitable with a higher purity boron powder (99%)being preferred. The boron powder may be milled to reduce its particlesize. The boron may be used in any way disclosed in U.S. Nonprovisionalapplication Ser. Nos. 13/768,219 and 13/749,794.

Also, the precursor mixture, including any fibers, may be formed into ashaped component. The component may be shaped and/or heated underpressure, removed from the pressure, and heated to thermoset and ceramiccomponents as described below.

The precursor mixture, which may be mixed in a melt stage, thenundergoes a heating step to form a thermoset composition. This may beperformed while the mixture is in a mold. This will allow the finalproduct to have the same shape as the mold, as the organic component ofthe mixture will melt if not already liquid and the mixture will fillthe mold during the heating, and retain its shape when the ceramic isformed. The precursor mixture is heated in an inert atmosphere at atemperature that causes polymerization of the organic compound to athermoset. If the organic compound is volatile, the heating may beperformed under pressure, either physical or gas pressure, to avoidevaporation of the organic compound. Suitable heating temperaturesinclude, but are not limited to, 150-500° C. or 700° C.

Heating the precursor may also cause the polymerization of the organiccompound to a thermoset. The silicon particles 10 would then bedispersed throughout the thermoset 20 as shown in FIG. 2. A thermosethaving the silicon particles dispersed throughout may be used as a finalproduct. The thermoset may also be machined to a desired shape, followedby heating to form a ceramic as described below.

The silicon may be homogeneously distributed or embedded in thethermoset as an intermediate shaped solid. At this stage, thecomposition may have a shape that it will retain upon further heatingand conversion to the ceramic from reaction of the silicon with thedeveloping carbon matrix.

The precursor mixture may be consolidated to a shaped solid componentunder pressure to promote intimate contact of the reactants to provide avery dense ceramic solid or to densify the final product. The precursormixture may be compacted under exterior pressure, removed from thepressure, and then heated to a thermoset followed by conversion to theceramic. Alternatively, the precursor mixture may be compacted underexterior pressure and the pressure maintained while heating to thethermoset and ceramic.

Optionally, the thermoset composition may be heated between 600 to 1400°C. The upper end of the range approaches the melting point of silicon.These temperatures may produce carbonization of the organic precursor toproduce a silicon-carbon composition in which the silicon is embedded inthe carbon waiting to react at or above the melting point of thesilicon.

In a second heating step, the thermoset composition is heated to form aceramic. The heating is performed at a temperature that causes formationof nanoparticles of silicon carbide 60 in a carbonaceous matrix orsilicon matrix 70 (FIG. 4). The carbonaceous matrix may comprisegraphitic carbon, carbon nanotubes, and/or amorphous carbon. If nitrogenis present, silicon nitride nanoparticles may be formed. There may be ahigher concentration of nitrides on the surface than in the interior.Suitable heating temperatures include, but are not limited to 500-1900°C. If boron is present, then silicon boron carbide nanoparticles may beformed.

The presence and composition of the silicon carbide or silicon nitridenanoparticles may be verified by any known technique for detectingnanoparticles such as SEM, TEM, or XRD. The nanoparticles may have anaverage diameter of less than 100 nm, 50 nm, or 30 nm. They may begenerally spherical in shape or may be non-spherical, such as nanorodsor other nanostructures.

The ceramic may include any amount of nanoparticles and/or nanorods,including but not limited to, at least 5%, 10%, 20%, 30%, 40%, 50%, 60%,70%, 80%, 90%, 95%, or 99% by weight of nanoparticles. The percentage ofnanoparticles and/or nanorods may be in part determined by the molarratio of silicon and carbon atoms in the precursor mixture. At a 1:1ratio, nearly all of the silicon and carbon may be incorporated into thenanoparticles/nanorods (nanostructures), leaving a small amount or traceof carbonaceous matrix or silicon matrix. With higher amounts of organiccompound, the fraction of silicon carbide nanostructures is lower andthe fraction of matrix is higher. By this method, variations in theratio of silicon to organic may be used, affording a mixture of siliconcarbide and matrix when performed in an inert atmosphere such as argonand silicon carbide, silicon nitride, and matrix when performed in anitrogen atmosphere. When silicon nitride is made, raising the amount ofcarbon in the precursor mixture may lower the amount of silicon nitridein the ceramic.

The ceramic is not formed as a powder and may be in the form of a solid,unbroken mass. It may contain less than 20% by volume of voids or as lowas 10%, 5%, or 1%. It may have the same shape as the precursor mixture(if solid) or it may take on the shape of a mold it was placed in duringthe heating. The ceramic may retain its shape in that it does notcrumble when handled and may not change shape or break without the useof extreme force. The ceramic composition may be tough, hard, and havestructural integrity. The degree of such properties may depend on theamount of ceramic to carbon in the solid ceramic composition. Any shapemay be formed to make an article useful for incorporation into anapparatus. The article may be large enough to have a minimum size of atleast 1 cm in all dimensions. That is, the entire surface of the articleis at least 5 mm from the center of mass of the article. Larger articlesmay be made, such as having a minimum size of at least 10 cm in alldimensions. Also, the composition may have smaller sizes, such as 1 mm,2 mm, or 5 mm.

The following examples are given to illustrate specific applications.These specific examples are not intended to limit the scope of thedisclosure in this application. Any other appropriate methods andmaterials disclosed in U.S. Provisional Application Nos. 61/590,852;61/640,744; 61/669,201; and 61/693,930 and U.S. Nonprovisionalapplication Ser. Nos. 13/779,771; 13/768,219; and 13/749,794 may beused. Any carbon source, boron source, metal compound, and/or otherparameter disclosed therein may be used in any combination in thepresently disclosed method, and may be combined with any material and/orparameter disclosed in the present application.

EXAMPLE 1

Formulation of precursor composition of TPEB and silicon powder (1 to 5μm particle Size) in molar ratio of 1 to 50—TPEB (0.250 g; 0.523 mmol)and silicon powder (1 to 5 μm particle size) (0.732 g, 26.1 mmol) werethoroughly mixed and used as the precursor composition for the formationof refractory nanoparticle SiC embedded or bonded with the excess ofsilicon that behaves as a matrix material. The ratio of the tworeactants can be readily varied by the described formulation method.

EXAMPLE 2

Conversion of precursor composition of TPEB and silicon powder (1 to 5μm particle size) in molar ratio of 1 to 50 to polymeric thermoset solidin an argon atmosphere—A sample (75.2450 mg) of the precursorcomposition of Example 1 was weighed into a TGA ceramic pan, packedthoroughly, flushed with flow (110 cc/min) of argon for 20 minutes, andthen heated at 5° C./min to 250° C. and held at this temperature for 1hr to consolidate to a shaped thermoset solid from reaction of theethynyl units of TPEB.

EXAMPLE 3

Conversion of polymeric thermoset solid to shaped siliconcarbide-Silicon Matrix Solid Ceramic Composition by Heating to 1450° C.under an argon atmosphere—The solid polymeric thermoset of Example 2 washeated under a flow (110 cc/min) of argon at 3° C./min to 1200° C. andheld at this temperature for 1 min followed by heating at 1° C./min to1415° C. and holding at this temperature for 1 hr and at 1 ° C./min to1450° C. and holding at this temperature for 1 hr. The resulting solidceramic sample retained 90.45% of the original weight. XRD analysisshowed the formation of pure silicon carbidenanoparticles/nanostructures embedded in a matrix of crystalline Sinanostructure.

EXAMPLE 4

Conversion of precursor composition of TPEB and silicon powder (1 to 5μm particle size) in molar ratio of 1 to 50 to polymeric thermoset solidin an nitrogen atmosphere—A sample (71.1040 mg) of the precursorcomposition of Example 1 was weighed into a TGA ceramic pan, packedthoroughly, flushed with flow (110 cc/min) of nitrogen for 20 minutes,and then heated at 5° C./min to 250° C. and held at this temperature for1 hr to consolidate to a shaped thermoset solid from reaction of theethynyl units of TPEB.

EXAMPLE 5

Conversion of polymeric thermoset solid to shaped siliconcarbide/silicon nitride solid ceramic composition by heating to 1450° C.under a nitrogen atmosphere—The solid polymeric thermoset of Example 4was heated under a flow (110 cc/min) of nitrogen at 3° C./min to 1200°C. and held at this temperature for 1 min followed by heating at 1°C./min to 1415° C. and holding at this temperature for 1 hr and heatingat 1° C./min to 1450° C. and holding for 1.5 hr. XRD analysis showed theformation of pure silicon carbide and silicon nitridenanoparticles/nanostructures, which are embedded in an excess amount ofsilicon. The silicon nitride nanoparticles/nanostructures were formedmainly on the exterior part or outer surface of the sample, which wasexposed to the nitrogen. The silicon carbidenanoparticles/nanostructures were mainly formed on the interior portionof the sample.

EXAMPLE 6

Conversion of precursor composition of TPEB and silicon powder (1 to 5μm particle size) in molar ratio of 1 to 50 to polymeric thermoset solidin an argon atmosphere—Another sample (70.7440 mg) of the precursorcomposition of Example 1 was weighed into a TGA ceramic pan, packedthoroughly, flushed with flow (110 cc/min) of argon for 20 minutes, andthen heated at 5° C./min to 250° C. and held at this temperature for 1hr to consolidate to a shaped thermoset solid from reaction of theethynyl units of TPEB.

EXAMPLE 7

Conversion of polymeric thermoset solid to shaped siliconcarbide-silicon matrix solid ceramic composition by heating to 1450° C.under an argon atmosphere—The solid polymeric thermoset of Example 6 washeated under a flow (110 cc/min) of argon at 2° C./min to 1300° C. andheld at this temperature for 1 min followed by heating at 1° C./min to1450° C. and holding at this temperature for 3 hr. The resulting solidceramic sample retained 93.23% of the original weight of precursorcomposition of Example 6. XRD analysis showed the formation of puresilicon carbide nanoparticles/nanostructures (50%) of average particlesize of 18.6 nm embedded in a matrix of crystalline Si (50%) of averageparticle size of 26.3 nm.

EXAMPLE 8

Formulation of precursor composition of TPEB and silicon powder (1 to 5μm particle size) in molar ratio of 1 to 40—TPEB (0.500 g; 1.05 mmol)and silicon (1 to 5 μm particle size) (1.12 g, 40.0 mmol) werethoroughly mixed and used as the precursor composition for the formationof refractory SiC embedded or bonded within the solid ceramiccomposition. The ratio of the two reactants can be readily varied by thedescribed formulation method.

EXAMPLE 9

Conversion of precursor composition of TPEB and silicon powder (1 to 5μm particle size) in molar ratio of 1 to 40 to polymeric thermoset solidin an argon atmosphere—A sample (75.3080 mg) of the precursorcomposition of Example 8 was weighed into a TGA-DSC ceramic pan, packedthoroughly, flushed with flow (110 cc/min) of argon for 20 minutes, andthen heated at 5° C./min to 250° C. and held at this temperature for 1hr to consolidate to a shaped thermoset solid from reaction of theethynyl units of TPEB.

EXAMPLE 10

Conversion of polymeric thermoset solid to shaped siliconcarbide-silicon matrix solid ceramic composition by heating to 1450° C.under an argon atmosphere—The solid polymeric thermoset of Example 9 washeated under a flow (110 cc/min) of argon at 5° C./min to 1450° C. andheld at this temperature for 2 hr. At 823° C. and based on the originalamount of precursor composition in Example 9, the sample retained 93.40%by weight; the weight loss being due to carbonization of the thermosetof Example 9. At about 1410° C., the silicon has completely melted(endotherm) followed by a rapid exotherm attributed to the reaction ofthe silicon melt with the carbonizing solid. The melted Si was embeddedin the carbonaceous solid where intimate contact was present. Thereaction media was heated at 1450° C. for a total of 2 hr. Upon cooling,the SiC ceramic composition was found to be extremely hard. XRD analysis(FIG. 5) showed the formation of SiC (82%) nanoparticles/nanostructuresof average size of 33 nm embedded in a silicon matrix (18%) of averageparticle size of 44 nm. The experiment was designed to have an excess ofsilicon to bind the SiC nanoparticles/nanostructures.

EXAMPLE 11

Conversion of precursor composition of TPEB and silicon powder (1 to 5μm particle size) in molar ratio of 1 to 40 to polymeric thermoset solidin a nitrogen atmosphere—A sample (66.7550 mg) of the precursorcomposition of Example 8 was weighed into a TGA-DSC ceramic pan, packedthoroughly, flushed with flow (110 cc/min) of nitrogen for 20 minutes,and then heated at 5° C./min to 250° C. and held at this temperature for1 hr to consolidate to a shaped thermoset solid from reaction of theethynyl units of TPEB.

EXAMPLE 12

Conversion of polymeric thermoset solid to shaped siliconcarbide-silicon nitride silicon matrix solid ceramic composition byheating to 1450° C. under a nitrogen atmosphere—The solid polymericthermoset of Example 11 was heated under a flow (110 cc/min) of nitrogenat 5° C./min to 1450° C. and held at this temperature for 1 hr. At 1047°C. and based on the original amount of precursor composition in Example11, the sample retained 93.09% by weight but commenced to slowlyincrease in weight due to reaction of the nitrogen with the Si. At about1418° C., the silicon was completely melted (endotherm) followed by arapid exotherm attributed to the fast reaction of the silicon melt withthe gaseous nitrogen and carbon. At 1450° C., the weight of the samplewas 108.2%. After 1 hr at 1450° C., the sample had taken on about 15%weight attributed to the formation of silicon nitride (Si₃N₄). Uponcooling, the SiC—Si₃N₄ ceramic composition was found to be extremelyhard. XRD analysis (FIG. 6) showed the large formation of SiCnanoparticles/nanostructures of particle size of 22 nm and Si₃N₄nanoparticles/nanostructures of particle size of 29 nm.

EXAMPLE 13

Conversion of precursor composition of TPEB and silicon powder (1 to 5μm particle size) in molar ratio of 1 to 40 to polymeric thermoset solidin an argon atmosphere—A sample (26.4840 mg) of the precursorcomposition of Example 8 was weighed into a TGA-DSC ceramic pan, packedthoroughly, flushed with flow (110 cc/min) of argon for 20 minutes, andthen heated at 5° C./min to 250° C. and held at this temperature for 1hr to consolidate to a shaped thermoset solid from reaction of theethynyl units of TPEB.

EXAMPLE 14

Conversion of polymeric thermoset solid to shaped siliconcarbide-silicon matrix solid ceramic composition by heating to 1450° C.under an argon atmosphere—The solid polymeric thermoset of Example 13was heated under a flow (110 cc/min) of argon at 3° C./min to 1300° C.and held at this temperature for 3 hr and retained 91.17% of weightbased on the original precursor weight of Example 13. XRD analysisshowed only a small amount of SiC formation and mostly crystalline Siremaining; the reaction of solid Si with carbon did not occur veryreadily in the solid phase indicating the importance of the reactionoccurring in the Si melt.

EXAMPLE 15

Formulation of precursor composition of TPEB and silicon powder (1 to 5μm particle size) in molar ratio of 1 to 30—TPEB (0.647 g; 1.35 mmol)and silicon (1 to 5 μm particle size) (1.12 g, 40.0 mmol) werethoroughly mixed and used as the precursor composition for the formationof refractory nanoparticle SiC in a solid ceramic composition. The ratioof the two reactants can be readily varied by the described formulationmethod.

EXAMPLE 16

Conversion of precursor composition of TPEB and silicon powder (1 to 5μm particle size) in molar ratio of 1 to 30 to polymeric thermoset solidin an argon atmosphere—A sample (65.2300 mg) of the precursorcomposition of Example 15 was weighed into a TGA-DSC ceramic pan, packedthoroughly, flushed with flow (110 cc/min) of argon for 20 minutes, andthen heated at 5° C./min to 250° C. and held at this temperature for 1hr to consolidate to a shaped thermoset solid from reaction of theethynyl units of TPEB.

EXAMPLE 17

Conversion of polymeric thermoset solid to shaped siliconcarbide-silicon matrix solid ceramic composition by heating to 1450° C.under an argon atmosphere—The solid polymeric thermoset of Example 16was heated under a flow (110 cc/min) of argon at 5° C./min to 1350° C.and held at this temperature for 1 minute followed by heating at 1°C./min to 1405° C. and holding at this temperature for 90 minutes, at 1°C./min to 1415° C. and holding at this temperature for 30 minutes, andfinally at 1° C./min 1430° C. and holding at this temperature for 30minutes. Based on the original precursor composition of Example 16, theceramic solid retained 89.88% by weight. Upon cooling, the SiCcontaining solid was found to be extremely hard. XRD analysis (FIG. 7)showed the formation of SiC nanoparticles/nanostructures (91%) with anaverage particle size of 22 nm embedded in excess silicon matrix (9%)with an average particle size of 35 nm. FIG. 8 shows an SEM of a typicalsample.

EXAMPLE 18

Conversion of precursor composition of TPEB and silicon powder (1 to 5μm particle size) in molar ratio of 1 to 30 to polymeric thermoset solidin an argon atmosphere—Another sample (68.8260 mg) of the precursorcomposition of Example 15 was weighed into a TGA-DSC ceramic pan, packedthoroughly, flushed with flow (110 cc/min) of argon for 20 minutes, andthen heated at 5° C./min to 250° C. and held at this temperature for 1hr to consolidate to a shaped thermoset solid from reaction of theethynyl units of TPEB.

EXAMPLE 19

Conversion of polymeric thermoset solid to shaped siliconcarbide-silicon matrix solid ceramic composition by change of heattreatment to 1450° C. under an argon atmosphere—The solid polymericthermoset of Example 18 was heated under a flow (110 cc/min) of argon at2° C./min to 1150° C. and held at this temperature for 1 minute followedby heating at 1° C./min to 1405° C. and holding at this temperature for1 hr, at 1° C./min to 1415° C. and holding at this temperature for 1 hr,and finally heating at 1° C./min to 1430° C. and holding at thistemperature for 1 hr. Based on the original precursor composition ofExample 18, the ceramic solid retained 90.14% by weight. Upon cooling,the SiC containing solid ceramic was found to be extremely hard. XRDanalysis (FIG. 9) showed the formation of SiCnanoparticles/nanostructures (91%) with an average particle size of 23nm embedded in excess, unreacted silicon matrix (9%) with an averageparticle size of 28 nm. The experiment was designed to have an excess ofsilicon to bind the SiC nanoparticles/nanostructures and for thereaction to occur under more controlled conditions.

EXAMPLE 20

Conversion of precursor composition of TPEB and silicon powder (1 to 5μm particle size) in molar ratio of 1 to 30 to polymeric thermoset solidin an argon atmosphere—Another sample (78.4630 mg) of the precursorcomposition of Example 15 was weighed into a TGA-DSC ceramic pan, packedthoroughly, flushed with flow (110 cc/min) of argon for 20 minutes, andthen heated at 5° C./min to 250° C. and held at this temperature for 1hr to consolidate to a shaped thermoset solid from reaction of theethynyl units of TPEB.

EXAMPLE 21

Conversion of polymeric thermoset solid to shaped siliconcarbide-silicon matrix solid ceramic composition by change of heattreatment to 1450° C. under an argon atmosphere—The solid polymericthermoset of Example 20 was heated under a flow (110 cc/min) of argon at2° C./min to 1300° C. and held at this temperature for 1 minute followedby heating at 1° C./min to 1450° C. and holding at this temperature for3 hr. Based on the original precursor composition of Example 20, theceramic solid retained 89.54% by weight. Upon cooling, the gray SiCcontaining ceramic solid was found to be extremely hard. XRD analysisshowed the formation of SiC nanoparticles/nanostructures (95%) with anaverage particle size of 25 nm embedded in excess, unreacted siliconmatrix (5%) with an average particle size of 12.1 nm.

EXAMPLE 22

Formulation of precursor composition of TPEB and silicon powder in molarratio of 1 to 21—TPEB (0.910 g; 1.90 mmol) and silicon (1 to 5 μmparticle size) (1.12 g, 40.0 mmol) were thoroughly mixed and used as theprecursor composition for the formation of refractory nanoparticle SiCembedded or bonded with the excess of carbon that behaves as a matrixmaterial. The ratio of the two reactants can be readily varied by thedescribed formulation method.

EXAMPLE 23

Conversion of precursor composition of TPEB and silicon powder (1 to 5μm particle size) in molar ratio of 1 to 21 to polymeric thermoset solidin an argon atmosphere—A sample (67.0020 mg) of the precursorcomposition of Example 22 was weighed into a TGA-DSC ceramic pan, packedthoroughly, flushed with flow (110 cc/min) of argon for 20 minutes, andthen heated at 5° C./min to 250° C. and held at this temperature for 1hr to consolidate to a shaped thermoset solid from reaction of theethynyl units of TPEB.

EXAMPLE 24

Conversion of polymeric thermoset solid to shaped silicon carbide-carbonmatrix solid ceramic composition by heating to 1450° C. under an argonatmosphere—The solid polymeric thermoset of Example 23 was heated undera flow (110 cc/min) of argon at 2° C./min to 1150° C. and held at thistemperature for 1 minute followed by heating at 1° C./min to 1405° C.and holding at this temperature for 1 hr, heating at 1° C./min to 1415°C. and holding at this temperature for 1 hr, and finally heating at 1°C./min 1430° C. and holding at this temperature for 1 hr. Based on theoriginal precursor composition of Example 23, the ceramic solid retained87.24% by weight. Upon cooling, the SiC containing ceramic solid wasfound to be extremely hard. XRD analysis (FIG. 10) showed the formationof SiC nanoparticles/nanostructures (100%) with an average particle sizeof 22 nm embedded in small amount of amorphous carbon. The experimentwas designed to have an excess of carbon to bind the SiC nanoparticles.

EXAMPLE 25

Formulation of precursor composition of TPEB and silicon powder in molarratio of 1 to 10—TPEB (0.250 g; 0.523 mmol) and silicon (1 to 5 μmparticle size) (0.146 g, 5.21 mmol) were thoroughly mixed and used asthe precursor composition for the formation of refractory nanoparticleSiC embedded or bonded with the excess of carbon that behaves as amatrix material. The ratio of the two reactants can be readily varied bythe described formulation method.

EXAMPLE 26

Conversion of precursor composition of TPEB and silicon powder (1 to 5μm particle size) in molar ratio of 1 to 10 to polymeric thermoset solidin an argon atmosphere—A sample (57.3190 mg) of the precursorcomposition of Example 25 was weighed into a TGA-DSC ceramic pan, packedthoroughly, flushed with flow (110 cc/min) of argon for 20 minutes, andthen heated at 5° C./min to 250° C. and held at this temperature for 1hr to consolidate to a shaped thermoset solid from reaction of theethynyl units of TPEB.

EXAMPLE 27

Conversion of polymeric thermoset solid to shaped silicon carbide-carbonmatrix solid ceramic composition by heating to 1450° C. under an argonatmosphere—The solid polymeric thermoset of Example 26 was heated undera flow (110 cc/min) of argon at 3° C./min to 1200° C. and held at thistemperature for 1 minute and then heated at 1° C./min to 1450° C. andheld at this temperature for 3 hr. Upon cooling, the SiC-carbon matrixcomposition was found to be tough and gray in color. The experiment wasdesigned to have an excess of carbon to bind the SiCnanoparticles/nanostructures.

EXAMPLE 28

Conversion of precursor composition of TPEB and silicon powder (1 to 5μm particle size) in molar ratio of 1 to 10 to polymeric thermoset solidin an nitrogen atmosphere—A sample (56.0440 mg) of the precursorcomposition of Example 25 was weighed into a TGA-DSC ceramic pan, packedthoroughly, flushed with flow (110 cc/min) of nitrogen for 20 minutes,and then heated at 5° C./min to 250° C. and held at this temperature for1 hr to consolidate to a shaped thermoset solid from reaction of theethynyl units of TPEB.

EXAMPLE 29

Conversion of polymeric thermoset solid to shaped siliconcarbide-silicon nitride carbon matrix solid ceramic composition byheating to 1450° C. under a nitrogen atmosphere—The solid polymericthermoset of Example 28 was heated under a flow (110 cc/min) of nitrogenat 3° C./min to 1200° C. and held at this temperature for 1 minute andat 1° C./min to 1450° C. and held at this temperature for 3 hr. Thesample contained an excess of carbon in which the SiC and Si₃N₄nanoparticles/nanostructures were embedded. Upon cooling, the SiC—Si₃N₄carbon ceramic solid composition was found to be hard and tough.

EXAMPLE 30

Formation of silicon powder and TPEB carbon fiber polymeric composite inan argon atmosphere—Into a 1.0″ diameter mold fabricated from aluminumfoil was placed a precursor composition (2.6527 g of powdered siliconand TPEB mixture) prepared as in Example 25 and a small amount ofchopped carbon fibers was added and mixed. The composition was packedand heated to 240° C. to melt the TPEB and the melted composition waspressed with a flat surface to consolidate the sample to a flat surface.The resulting carbon fiber-precursor composition was heated under a flowof argon at 260-270° C. for 1 hr resulting in solidification to a solidcarbon fiber-containing polymeric thermoset. The solid carbon fiberpolymeric composite with a homogeneous distribution of the siliconpowder was removed from the mold.

EXAMPLE 31

Conversion of the silicon powder-carbon fiber polymeric composite tosolid silicon carbide carbon-carbon fiber ceramic composite in an argonatmosphere—The shaped solid carbon fiber polymeric composite prepared inExample 30 was placed in an oven and heated under a flow of argon at 3°C./min to 1450° C. and held at this temperature for 3 hr. The resultingceramic (SiC)-carbon-carbon fiber reinforced solid ceramic composite wascooled and appeared hard and tough.

EXAMPLE 32

Formation of silicon powder and TPEB carbon fiber polymeric composite inan argon atmosphere—Into a 1.0″ diameter mold fabricated from aluminumfoil was placed a precursor composition (2.8534 g of powdered siliconand TPEB mixture) prepared as in Example 15 and a small amount ofchopped carbon fibers was added and mixed. The composition was packedand heated under a flow of argon to 250° C. to melt the TPEB and themelted composition was pressed with a flat surface to consolidate thesample to a flat surface. The resulting carbon fiber-precursorcomposition was heated under a flow of argon at 260-270° C. for 1 hrresulting in solidification to a solid carbon fiber-containing polymericthermoset. The solid carbon fiber polymeric composite with a homogeneousdistribution of the silicon powder was removed from the mold.

EXAMPLE 33

Conversion of the silicon powder carbon fiber polymeric composite tosolid shaped silicon carbide carbon fiber ceramic composite in an argonatmosphere—The solid shaped carbon fiber polymeric composite prepared inExample 32 was placed in an oven and heated under a flow of argon at 3°C./min to 1450° C. and held at this temperature for 3 hr. The resultingceramic (SiC)-silicon matrix-carbon fiber reinforced solid ceramiccomposite appeared hard and tough.

EXAMPLE 34

Formulation of prepolymer composition of TPEB—TPEB (10.30 g; 21.5 mmol)was placed in an aluminum planchet and heated at 260° C. for 40 minutesor until the mixture was viscous to stir with a metal spatula. Themixture was cooled, broken into small pieces, and ball milled for 2minutes resulting in a fine black powder.

EXAMPLE 35

Formulation of precursor composition of silicon, boron, and TPEBprepolymer and formation of shaped pellet—TPEB prepolymer form Example34 (0.200 g; 0.418 mmol), boron (0.088 g, 8.14 mmol), and silicon (0.240g; 8.54 mmol) were ball milled for 5 minutes resulting in a deepred-black fine powder. The powder was placed in a 13 mm pellet press andpressed to 12,000 pounds for 1 minute.

EXAMPLE 36

Conversion of precursor composition of silicon, boron, and TPEBprepolymer to solid shaped thermoset—The pellet from Example 35 wasplaced in a furnace, heated at 20° C./min under an argon atmosphere to200° C., and held at this temperature for 10 hr (overnight) resulting inthe formation of a tough shaped polymeric thermoset solid. The siliconand boron were homogeneously dispersed in the solid thermoset.

EXAMPLE 37

Conversion of precursor composition of silicon, boron, and TPEBprepolymer to solid shaped thermoset—Another pellet prepared as inExample 35 was placed in a furnace, heated at 20° C./min under an argonatmosphere to 250° C., and held at this temperature for 2 hr resultingin the formation of a tough shaped polymeric thermoset solid.

EXAMPLE 38

Formation of refractory SiC solid ceramic in one step by heating at 2°C./min to 1600° C. under an argon atmosphere—The shaped polymericthermoset solid (0.522 g) from Example 36 was placed in a 3″ tubefurnace, heated at 2° C./min under a flow (100 cc/min) of argon to 1600°C., and held at 1600° C. for 2 hr yielding a solid dense ceramic (FIG.11) with weight retention of 92.8%. The solid ceramic was removed fromthe furnace, characterized by XRD, and found to form nanoparticle sizedSiC in an excess of carbon as the matrix and some silicon boron carbidephase. The SiC carbon solid composition was formed in one step andexhibited great structural integrity, hardness, and toughness. SEMimages (FIG. 12) show the formation of SiC nanoparticles and nanorodsbeing formed in the ceramic solid.

EXAMPLE 39

Formulation of precursor composition of silicon, boron, and TPEBprepolymer, formation of shaped pellet, and direct conversion torefractory SiBC solid ceramic carbon composition in one step—TPEBprepolymer (0.200 g; 0.418 mmol), prepared as in Example 34, boron(0.088 g, 8.14 mmol), and silicon (0.240 g; 8.54 mmol) were ball milledfor 5 minutes resulting in a deep red-black fine powder. The powder wasplaced in a 13 mm pellet press and pressed to 10,000 pounds for 1minute. The pellet was then placed in a furnace, heated at 20° C./minunder an argon atmosphere to 250° C., and held at this temperature for30 minutes followed by heating at 2° C./min under a flow (100 cc/min) ofargon to 1500° C. and holding at 1500° C. for 2 hr yielding a soliddense ceramic with weight retention of 92.4%. Upon cooling, the solidceramic was removed from the furnace, characterized by XRD, and found toform nanoparticle sized SiC in an excess of carbon as the matrix with asilicon boron carbon phase. The SiC carbon solid composition was formedin one step and exhibited great structural integrity, hardness, andtoughness.

EXAMPLE 40

Formulation of precursor composition of silicon and TPEB Prepolymer andpellet formation—TPEB prepolymer from Example 34 (0.200 g; 0.418 mmol)and silicon powder (0.246 g; 8.75 mmol) were ball milled for 5 minutesresulting in a deep red-black fine powder. The powder was placed in a 13mm pellet press and pressed to 10,000 pounds for 10 sec.

EXAMPLE 41

Conversion of precursor composition of silicon and TPEB prepolymer tosolid shaped thermoset—The pellet from Example 40 was placed in afurnace, heated at 20° C./min under an argon atmosphere to 215° C., andheld at this temperature for 10 hr (overnight) resulting in theformation of a tough shaped polymeric solid. The silicon powder washomogeneously dispersed in the solid thermoset.

EXAMPLE 42

Formation of refractory SiC solid ceramic in one step by heating at 2°C./min to 1500° C. under an argon atmosphere—The cured thermoset pellet(0.435 g) from Example 41 was placed in a 3″ tube furnace, heated at 2°C./min under a flow (100 cc/min) of argon to 1500° C., and held at 1500°C. for 2 hr yielding a solid dense ceramic with weight retention of85.0%. Upon cooling, the solid ceramic was removed from the furnace,characterized by XRD, and found to form nanoparticle sized pure SiC inan excess of carbon as the matrix. All of the silicon had reacted. TheSiC carbon solid composition was formed in one step and exhibitedstructural integrity, hardness, and toughness.

EXAMPLE 43

Formulation of precursor composition of silicon and TPEB prepolymer andpellet formation—TPEB prepolymer from Example 34 (0.200 g; 0.418 mmol)and silicon powder (0.239 g; 8.53 mmol) were ball milled for 5 minutesresulting in a deep red-black fine powder. The powder was placed in a 6mm pellet press and pressed to 4,000 pounds for 10 sec.

EXAMPLE 44

Conversion to polymeric thermoset solid follow by heat treatment toshaped silicon carbide-silicon matrix solid ceramic composition byheating to 1430° C. under an argon atmosphere—The pellet from Example 43was heated under a flow (100 cc/min) of argon at 5° C./min to 250° C.and held at 250° C. for 1 hr (conversion to solid thermoset) followed byheating at 3° C./min to 1200° C. and holding at 1200° C. for 1 minutefollowed by heating at 1° C./min to 1405° C. and holding at thistemperature for 1 hr, heating at 1° C./min to 1415° C. and holding atthis temperature for 1 hr, at 1° C./min to 1415° C. and holding at thistemperature for 1 hr and finally heating at 1° C./min to 1430° C. andholding at this temperature for 1 hr. Based on the original precursorcomposition of the pellet (85.6997 mg), the ceramic solid retained90.14% by weight. Upon cooling, the SiC containing solid ceramic (FIG.13) was found to be extremely hard. XRD analysis (FIG. 14) showed theformation of pure beta nanosized SiC (100%) with an average particlesize of 17.6 nm and 0% strain. The experiment was designed to formbasically pure SiC nanoparticles/nanostructures and for the reaction tooccur slowly above the melting point of silicon to control theexothermic reaction involving the formation of silicon carbide.

EXAMPLE 45

Formulation of precursor composition of silicon and TPEB prepolymercontaining chopped fibers—TPEB prepolymer from Example 34 (3.72 g; 7.78mmol) and silicon (4.46 g; 158 mmol) were ball milled for 5 minutesresulting in a deep red-black fine powder. Chopped carbon fibers (1.00g, ¼″ length) were added and the solid mixture was placed in 100 mL ofacetone and stirred for 6 hr. The solvent was removed and the solidmixture was placed in a 2½″ pellet die and pressed to 10,000 pounds for1 minute.

EXAMPLE 46

Conversion of precursor composition of silicon and TPEB prepolymercontaining chopped fibers to thermoset—The 2½″ pellet from Example 45was placed in a furnace, heated at 20° C./min under an argon atmosphereto 210° C., and held at this temperature for 10 hr (overnight) resultingin the formation of a tough shaped polymeric carbon fiber reinforcedthermoset solid. The silicon powder was homogeneous dispersed in thesolid thermoset-carbon fiber composite.

EXAMPLE 47

Formation of refractory carbon fiber reinforced SiC solid ceramic in onestep by heating at 2° C./min to 1500° C. under an argon atmosphere—Thecarbon fiber-containing shaped polymeric thermoset pellet (15.7 g) fromExample 46 was placed in a 3″ tube furnace and heated at 2° C./min undera flow (100 cc/min) of argon to 1400° C. and held at 1400° C. for 5minutes followed by heating at 0.2° C./min to 1500° C. and holding at1500° C. for 2 hr yielding a solid dense carbon fiber reinforced ceramic(FIG. 15) with weight retention of 90%. Upon cooling, the solid carbonfiber reinforced ceramic was removed from the furnace, characterized byXRD, and found to form nanoparticle sized SiC in the carbon-carbon fibercomposite. The SiC carbon-carbon fiber solid composition exhibited greatstructural integrity with the inclusion of the fiber reinforcement.

Obviously, many modifications and variations are possible in light ofthe above teachings. It is therefore to be understood that the claimedsubject matter may be practiced otherwise than as specificallydescribed. Any reference to claim elements in the singular, e.g., usingthe articles “a,” “an,” “the,” or “said” is not construed as limitingthe element to the singular.

What is claimed is:
 1. A composition comprising: nanoparticles ofsilicon carbide; and a carbonaceous matrix; wherein the compositioncomprises at least 30% by weight of the nanoparticles; wherein thecomposition is not in the form of a powder; and wherein the compositionis thermally stable at 3000° C.
 2. The composition of claim 1, whereinthe composition comprises at least 99% by weight of the nanoparticles.3. The composition of claim 1, wherein the average diameter of thenanoparticles is less than 100 nm.
 4. The composition of claim 1,wherein the nanoparticles comprise α-SiC.
 5. The composition of claim 1,wherein the nanoparticles comprise β-SiC.
 6. The composition of claim 1,wherein the carbonaceous matrix comprises graphitic carbon, carbonnanotubes, or amorphous carbon.
 7. The composition of claim 1, whereinthe composition further comprises: nanoparticles comprising siliconnitride.
 8. The composition of claim 1, wherein the composition furthercomprises: nanoparticles comprising silicon boron carbide.
 9. Thecomposition of claim 1, wherein the composition further comprises:fibers, carbon fibers, ceramic fibers, or metal fibers.
 10. Thecomposition of claim 1, wherein the composition contains less than 20%by volume of voids.
 11. An article comprising the composition of claim1, wherein the article is in the form of a solid, unbroken mass having aminimum size of at least 1 mm in all dimensions.
 12. A compositioncomprising: nanoparticles of silicon carbide; and a silicon matrix;wherein the composition comprises at least 70% by weight of thenanoparticles or the average diameter of the nanoparticles is less than100 nm; and wherein the composition is not in the form of a powder. 13.The composition of claim 12, wherein the composition comprises at least70% by weight of the nanoparticles.
 14. The composition of claim 12,wherein the composition comprises at least 99% by weight of thenanoparticles.
 15. The composition of claim 12, wherein the averagediameter of the nanoparticles is less than 50 nm.
 16. The composition ofclaim 12, wherein the nanoparticles comprise α-SiC.
 17. The compositionof claim 12, wherein the nanoparticles comprise β-SiC.
 18. Thecomposition of claim 12, wherein the composition further comprises:nanoparticles comprising silicon nitride.
 19. The composition of claim12, wherein the composition further comprises: nanoparticles comprisingsilicon boron carbide.
 20. The composition of claim 12, wherein thecomposition further comprises: fibers, carbon fibers, ceramic fibers, ormetal fibers.
 21. The composition of claim 12, wherein the compositioncontains less than 20% by volume of voids.
 22. An article comprising thecomposition of claim 12, wherein the article is in the form of a solid,unbroken mass having a minimum size of at least 1 mm in all dimensions.23. A composition comprising: nanoparticles of silicon carbide; and acarbonaceous matrix comprising graphitic carbon, carbon nanotubes, oramorphous carbon; wherein the composition is not in the form of apowder; and wherein the composition comprises at least 30% by weight ofthe nanoparticles.
 24. The composition of claim 23, wherein thecomposition further comprises: nanoparticles comprising silicon nitride.25. The composition of claim 23, wherein the composition furthercomprises: nanoparticles comprising silicon boron carbide.
 26. Thecomposition of claim 23, wherein the composition further comprises:fibers, carbon fibers, ceramic fibers, or metal fibers.
 27. An articlecomprising the composition of claim 23, wherein the article is in theform of a solid, unbroken mass having a minimum size of at least 1 mm inall dimensions.
 28. A composition comprising: nanoparticles of siliconcarbide; and a carbonaceous matrix or silicon matrix; wherein thecomposition is not in the form of a powder; and wherein thenanoparticles in the composition have a continuous grain structure. 29.The composition of claim 28, wherein the composition comprises at least5% by weight of the nanoparticles.
 30. The composition of claim 28,wherein the carbonaceous matrix comprises graphitic carbon, carbonnanotubes, or amorphous carbon.
 31. The composition of claim 28, whereinthe composition further comprises: nanoparticles comprising siliconnitride.
 32. The composition of claim 28, wherein the compositionfurther comprises: nanoparticles comprising silicon boron carbide. 33.The composition of claim 28, wherein the composition further comprises:fibers, carbon fibers, ceramic fibers, or metal fibers.
 34. An articlecomprising the composition of claim 28, wherein the article is in theform of a solid, unbroken mass having a minimum size of at least 1 mm inall dimensions.